The subject matter of this invention relates generally to circuit breakers and more specifically to electrically interconnected circuit breakers.
It is well known to provide electronic control systems for circuit breakers. An example of such a system is shown in U.S. Pat. No. 3,660,722 issued May 2, 1972 to J. T. Wilson et al. In the latter system, various control functions are provided. As an example, a short-time delay tripping circuit is provided, a long-time delay tripping function is provided, a ground fault current tripping function is provided and an instantaneous tripping function is provided. The long-time delay tripping circuit is utilized when the amount of overload current is only slightly larger than the rated current of the circuit breaker. In such a case, the tripping of the circuit breaker follows the wellknown I.sup.2 t= K relationship. In the case where the amount of overload current is substantially higher than the rated current of the circuit breaker, but not of such a catastrophic nature as to require instantaneous tripping, a short time-fixed delay before tripping is provided. In this case, a fixed predetermined time for tripping is initiated once the current reaches a predetermined value. If the current does not drop below that predetermined value within the short delay time the circuit breaker will trip. Of course, if the circuit breaker current reaches substantially higher current values which may be of a catastrophic nature the circuit breaker is tripped instantaneously. Another function of the control system is to provide circuit breaker tripping for ground fault currents of a predetermined magnitude. Ground fault currents generally are of a relatively low magnitude but are relatively dangerous because of the presence of electrical arcs between the system being protected and ground. As a result, ground fault circuit tripping control systems have been recently developed. An example of a ground fault control system is shown in U.S U.S. Pat. No. 3,733,517 issued May 15, 1973 to J. T. Wilson. In this case, ground fault current is sensed by an appropriate monitor and a control system connected thereto initiates actuation of the circuit breaker to remove the ground fault or to interrupt the line in which the ground fault is flowing. In conjunction with the latter system, apparatus was developed for electrically communicating between the ground fault tripping control system of a number of circuit breaker systems. In the latter case, output signals are provided from one circuit breaker to another to disable the ground fault tripping system of the latter circuit thus giving the former circuit breaker control system an opportunity to isolate the ground fault from the system or a portion thereof, without shutting down the entire system. The latter apparatus is explained in U.S. Pat. No. 3,697,810 issued Oct. 10, 1972 to J. T. Wilson et al. It is desirous in the art of circuit breaker control to actuate the opening of a circuit breaker only under the worst conditions. Electrical overloads, short circuits and faults are dangerous and undesirable, but on the other hand the closing down of an electrical system is also undesirable. It is desirous therefore to close down the electrical system as close to the fault as possible, as fast as possible without closing down the remaining sections of the system. For this reason the previously described short delay and long delay tripping functions have been implemented. The reasoning is that electrical apparatus or electrical conditions which may cause overloads to exist on systems to be protected may disappear or correct themselves after a period of time. Consequently, if the physical characteristics of the circuit breaker are such that the amount of overload current can be tolerated for that period of time, it is desirous to keep the circuit breaker on the line in hopes the condition which is causing the overload will be corrected. If the overload current is of a relatively low magnitude, the circuit breaker can stay on the line for a very long period of time. On the other hand, if the overload current is of a significantly higher value, the circuit breaker can stay on the line for only a shorter period of time. Of course a value of overload current may eventually be reached where the circuit breaker must open instantaneous to protect property and lives. As was described previously, each circuit breaker in a control system may have independent short delay and long delay sensing and control apparatus. Two, three, or even more circuit breakers may be connected in series in a line which is carrying overload or fault current. Because each of the control systems are independent, all of the control systems sense the overload or fault current and begin to react accordingly. It is known, that the fault or overload may be isolated in many cases merely by opening one of the circuit breakers. Consequently it is not necessary to open the other circuit breakers. The other circuit breakers may be controlling current which feeds lines which are not protected by the first circuit breaker and as a result, the opening of the latter circuit breakers will interfere with the operation of a normally operating portion of the electrical distribution system. Past designers of circuit breaker equipment have envisioned this and have thus provided long delay and short delay timing functions. These functions give a first circuit breaker an opportunity to clear the system of overload current. Naturally if the system is cleared, the long delay or short delay timing functions is aborted on an individual basis and the remainder of the distribution system continues to operate naturally. The same would be true if the fault were not cleared but the first circuit breaker remained opened. Of course, the above-mentioned cooperation is independent from circuit breaker to circuit breaker. It would be advantageous if backup control for the independent circuit breaker systems could be provided by electrically interconnecting them. In this way one circuit breaker system can be keyed to react in response to what is happening in another circuit breaker system. It would also be advantageous if the short delay tripping circuit and the long delay tripping circuit for subsequent circuit breakers could be disabled while a first circuit breaker tested the distribution system to see if its reaction to the flow of overload current cleared the entire system of fault current.